A genetic approach to the analysis of the cell cycle in Caulobacter crescentus is proposed. These gram negative bacteria divide unequally to give two daughter cells with different developmental pathways: a motile swarmer cell which develops into a new non-motile stalked cell, and a stalked cell which elongates and divides continuously to produce new swarmer cells from one pole. Conditional mutations that affect specific developmental steps in each of these two pathways will be isolated and characterized. From the phenotypes of these mutants it should be possible to deduce the genetic organization of different developmental pathways. These strains will also be used for biochemical studies now underway on development. The second part of the proposed project is an examination of the spatial and temporal control of differentiation using these mutants. Specifically, we plan to examine how the synthesis and localization of the flagellum and bacteriophage LC72 receptor sites are regulated in strains blocked in the DNA synthetic and cell division pathways. The LC72 surface sites are made at the time of cell division and located uniquely at the flagellated pole of the new swarmer cell. These two aspects of formation will be examined in the mutants grown under non-permissive conditions.